U.S. patent application number 10/488357 was filed with the patent office on 2005-02-17 for photoresponsive polymer systems and their use.
Invention is credited to Khodorkovsky, Vladimir, Vaganova, Eugenia, Yitzchaik, Shlomo.
Application Number | 20050038143 10/488357 |
Document ID | / |
Family ID | 26980340 |
Filed Date | 2005-02-17 |
United States Patent
Application |
20050038143 |
Kind Code |
A1 |
Yitzchaik, Shlomo ; et
al. |
February 17, 2005 |
Photoresponsive polymer systems and their use
Abstract
The present invention provides an organic composition comprising
a water-soluble heteroaromatic compound, water and a polymer
containing repeat units derived from six-membered aromatic
heterocyclic monomers substituted in the 4-position relative to the
heteroatom by an alkyl substituent, said six-membered aromatic
heterocyclic monomer optionally being further substituted. The
organic composition is excitable by predetermined incident
electromagnetic radiation of predetermined intensity such that the
excitation of a location of the composition by the predetermined
incident radiation creates at least one of the following effects: a
desired luminescence of the excited location and a desired
electrical conductivity of the excited location.
Inventors: |
Yitzchaik, Shlomo;
(Jerusalem, IL) ; Vaganova, Eugenia; (Jerusalem,
IL) ; Khodorkovsky, Vladimir; (Beer-Sheva,
IL) |
Correspondence
Address: |
NATH & ASSOCIATES
1030 15th STREET, NW
6TH FLOOR
WASHINGTON
DC
20005
US
|
Family ID: |
26980340 |
Appl. No.: |
10/488357 |
Filed: |
October 8, 2004 |
PCT Filed: |
September 4, 2002 |
PCT NO: |
PCT/IL02/00737 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60316278 |
Sep 4, 2001 |
|
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|
60402530 |
Aug 12, 2002 |
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Current U.S.
Class: |
524/99 |
Current CPC
Class: |
Y02E 10/549 20130101;
H01L 51/42 20130101; C08G 61/122 20130101; B82Y 10/00 20130101;
H01L 51/004 20130101; H01L 51/0595 20130101; H01L 51/0041 20130101;
H01L 51/428 20130101 |
Class at
Publication: |
524/099 |
International
Class: |
C08L 001/00 |
Claims
1. An organic composition comprising a water-soluble heteroaromatic
compound, and a polymer containing repeat units derived from
six-membered aromatic heterocyclic monomers substituted in the
4-position relative to the heteroatom by an alkyl substituent, said
six-membered aromatic heterocyclic monomer optionally being further
substituted, the organic composition being characterized in that it
also comprises water such that the molar ratio between the polymer,
the water-soluble heteroaromatic compound and water is about
1:1:(0.3-1.0), the composition being excitable by predetermined
incident electromagnetic radiation of predetermined intensity such
that the excitation of a location of the composition by the
predetermined incident radiation creates at least one of the
following effects: a desired luminescence of the excited location
and a desired electrical conductivity of the excited location.
2. The composition according to claim 1, being excitable by the
predetermined electromagnetic radiation in the ultraviolet or
visible spectrum range.
3. The composition according to claim 1, being excitable by the
predetermined electromagnetic radiation having a wavelength
selected of about 250 nm.
4. The composition according to claim 1, being sequentially
excitable by the electromagnetic radiation of at least two
different wavelengths, resulting in the at least one of desired
luminescence and desired conductivity of the sequentially excited
location in the composition.
5. The composition according to claim 1, being excitable by the
predetermined electromagnetic radiation to be shiftable between
different states of at least one of the desired luminescence and
desired electrical conductivity.
6. The composition according to claim 1, wherein the excited
location of the composition is responsive to the predetermined
electromagnetic radiation to be thereby returned to its passive,
non-luminescent state.
7. The composition according to claim 1, having an initial
conductivity, prior to applying the electromagnetic radiation
thereto, of about 10.sup.-9 Scm.sup.-1.
8. The composition according to claim 1, wherein said desired
conductivity is in a range between 10.sup.-6-10.sup.-3
Scm.sup.-1.
9. The composition according to claim 1, wherein said water-soluble
heteroaromatic compound is selected from the group comprising:
pyridine, substituted pyridine, pyrimidine, nicotine, quinoline,
substituted quinoline, adenine, bi-pyridine, derivatives thereof
and mixtures thereof.
10. The composition according to claim 1 wherein said polymer is
selected from optionally substituted poly(4-vinyl pyridine),
poly(4-vinyl quinoline) and co-polymers thereof.
11. An organic composition according to claim 1, comprising
poly(4-vinyl pyridine), pyridine and water in a molar ratio of
about 1:1:(0.3-1.0), the organic composition being responsive to
incident electromagnetic radiation of a predetermined wavelength
range such that irradiation of a location of the composition
creates a desired electrical conductivity of said location.
12. A composition according to claim 1, being excitable by the
predetermined incident electromagnetic radiation between its
passive non-luminescent state and active luminescent state, and
vice versa.
13. An optical device comprising a cell containing an organic
composition according to claim 1, said cell being shiftable between
stable states of different responses of said composition to
predetermined incident electromagnetic radiation.
14. The device according to claim 13, being operable as an optical
switch.
15. The device according to claim 13, being an information
carrier.
16. A transistor structure having an electrodes' arrangement and
the composition of claim 1 located in a space between the
electrodes, a semiconductor region of the transistor being the
excited location in said composition.
17. A method for treating an organic composition comprising a
water-soluble heteroaromatic compound, water, and a polymer
containing repeat units derived from six-membered aromatic
heterocyclic monomers substituted in the 4-position relative to the
heteroatom by an alkyl substituent, said six-membered aromatic
heterocyclic monomer optionally being further substituted, wherein
the molar ratio between the polymer, the water-soluble
heteroaromatic compound and water is about 1:1:(0.3-1.0), the
method comprising: (i) providing a viscous mixture of the
constituents as defined above; (ii) irradiating at least selected
locations of said viscous mixture with ultra-violet radiation
having a predetermined intensity so as to cause excitation in the
irradiated locations of said mixture to thereby obtain at least one
of desired luminescence or desired electrical conductivity of the
irradiated locations.
18. The composition according to claim 1, wherein excitation by
electromagnetic radiation having a wavelength of about 250 nm,
results in the formation of aminopentadienal and/or
polyazaacetylene in that composition.
Description
FIELD OF THE INVENTION
[0001] The present invention is generally in the field of
photoresponsive polymeric systems.
LIST OF REFERENCES
[0002] The following references are considered to be pertinent for
the purpose of understanding the background of the present
invention:
[0003] (1) H. Hong et al, Thin Solid Films 366, 260-264 (2000);
[0004] (2) W. Jessen et al, Synth. Metals 84, 501 (1997);
[0005] (3) E. Vaganova et al, "Photoinduced structure changes in
Poly (4-vinyl pyridine): a luminescence study"; Journal of
Fluorescence 10, 2, 81-88, (2000);
[0006] (4) U.S. Pat. No. 5,272,234;
[0007] (5) Vaganova, E., Yitzchaik, S. "Photoinduced reversible
cross-linking in polymeric matrices", Pol. Mat. Sci. Eng. 84,
1089-1090, 2001;
[0008] (6) Vaganova, E., Rozenberg, M., and Yitzchaik, S.
"Multicolor Emission in Poly(4-vinyl-pyridine) Gel", Chemistry of
Materials, 2000, 12, 261-263;
[0009] (7) Rozenberg, M., Vaganova, E., and Yitzchaik, S., "FTIR
Study of Self-Protonation and Gel Formation in Pyridinic solution
Poly(4-vinyl pyridine)", New Journal Chemistry, 2000, 24, 109-111;
and
[0010] (8) Vaganova, E. and Yitzchaik, S. "Tunable emission in
Poly(4-vinyl pyridine)-based Gel", Acta Polym., 1998, 49,
632-637.
BACKGROUND OF THE INVENTION
[0011] Polymers with tunable optical properties that may be varied
in predictable ways are of great interest for practical
applications, e.g. optical storage and retrieval devices.
[0012] One way to vary the optical properties of a polymer is to
change its chain packing order. Optical properties of
pyridine-containing polymers are well known as
morphology-dependent. The promotion of lone-pairs electrons to
backbone results in the broken charge conjugation symmetry. For
example, the photoluminescence of pyridine-containing polymers,
poly(p-pyridine) and poly(p-pyridyl-vinylene), was red shifted in
thin film compared to that in solution (W. Jessen et al, (1997)).
Interchain interactions in the film lead to the distribution of
electrons over wider parts of the molecule than in solution. Such
delocalization causes a reduction of the band gap and consequently
the photoluminescence is shifted to longer wavelengths.
[0013] A recent study (E. Vaganova et al, "Photoinduced structure
changes in Poly (4-vinyl pyridine): a luminescence study" Journal
of Fluorescence 10, 2, 81-88, (2000) teaches a manner of
controlling photoluminescence properties in a system based on
poly(4-vinyl pyridine) (hereinafter "P4VPy"). In this study,
concentrated solutions of P4VPy dissolved in pyridine turned into
gel under UV-irradiation, specifically, at 380 nm. This phase
transition results in changes in the optical properties of this
polymer. In the absorption spectrum, a new absorption appeared in
the visible range, and the position of the photoluminescence
maximum could be changed continuously from 440 nm to 480 nm during
irradiation. Solutions of P4VPy in pyrimidine showed similar
behavior. It was also observed in that study that the process of
photoinduced sol-gel transformation is reversible: mechanical
perturbation or heating could convert the gel back to a fluid
solution.
[0014] Well-known photochemical reaction is pyridine cleavage.
Under UV-irradiation at 250 nm wavelength pyridine in the presence
of water undergoes photoisomerization to a Dewar pyridine. As the
reaction continues, 5-amino-2,4-pentadienal (AP) is produced. AP
absorbs at 364 nm and reverts in the dark to pyridine with water
elimination (Joussot-Dubien, J. Tetrahedron Letters, 1967, 44,
4389-4390; Andre, J. C.; Niclause, M.; Joussot-Dubien, J.; Deglise,
X. J. of Chemical Education, 1977, 54, 387-388; Wiltzbach, K. E.;
Rausch, D. J. J. Am. Chem. Soc., 1970, 92, 2178-2179).
[0015] Organic light emitting diode (OLED) devices based on
self-assembled P4VPy with poly(N-vinyl carbazole) and
2-(4-biphenyl)-5-(4-tert-butylphen- yl)-1,3,4-oxidiazole was
reported (H. Hong et al, (2000)).
[0016] The main principle of conductivity is supposed to be an
electron conduction, which occurs through the extended
.pi.-conjugation. Conjugated conductive polymers, which are
photo-responsive upon ultra-violet or visible light irradiation,
are described in U.S. Pat. No. 5,272,234. The conductive polymers
are prepared from copolymerization of photo-responsive groups
containing heterocyclic monomers and 3-substituted heterocyclic
monomers with the substituent containing a flexible segment like an
alkyl group, ethoxyl group or siloxane group. The conductivity of
these polymers can be controlled reversibly by irradiation of
light.
SUMMARY OF THE INVENTION
[0017] There is a need in the art to facilitate inducing of
luminescence into selective locations in an initially
non-luminescent material in a reversible manner, as well as enable
inducing electrical conductivity of selective locations in an
initially non-conductive material, by providing an organic
composition and a method of treating this composition to provide
the desired properties thereof.
[0018] The present invention relates to an organic composition that
is responsive to incident electromagnetic radiation of a
predetermined wavelength such that energy bands defining a certain
energy gap are created in an irradiated location of the composition
thereby defining the luminescence and/or electrical conductivity of
the irradiated location.
[0019] Thus, according to one aspect of the present invention there
is provided an organic composition comprising a water-soluble
heteroaromatic compound, water and a polymer having repeating units
derived from six-membered aromatic heterocyclic monomers
substituted in the 4-position relative to the heteroatom by an
alkyl substituent, said six-membered aromatic heterocyclic monomer
optionally being further substituted, the organic composition being
excitable by predetermined incident electromagnetic radiation of
predetermined intensity such that the excitation of a location of
the composition creates at least one of the following effects: a
desired luminescence of the excited location, and a desired
electrical conductivity of the excited location.
[0020] The water-soluble heteroaromatic compound is selected from:
pyridine, substituted pyridine, pyrimidine, nicotine, quinoline,
bi-pyridine, derivatives of these compounds and mixtures thereof.
More preferably, the compound is pyridine. The polymer may be
optionally substituted poly(4-vinyl pyridine),
poly(diallyldimethylamonium) chloride, poly(4-vinyl quinoline) or
co-polymers thereof, preferably poly(4-vinyl pyridine). The molar
ratio between the polymeric units, the water-soluble heteroaromatic
compound and water is preferably about 1:1:(0.3-1).
[0021] By appropriate radiation of a location in the composition
(where the term "appropriate" relates to a certain wavelength of
UV-radiation, intensity, and duration), the irradiated location can
be shifted from a stable initial state (substantially of only blue
luminescence) into a new, active state of desired luminescence, and
can be either returned into the initial state or to another state
of a different luminescence by a further application of
electromagnetic radiation of a predetermined wavelength to this
location. Irradiation of a selected location of the composition can
shift this location from its passive state (where the term "passive
state" used herein denotes a state of substantially
low-conductivity) into an active stable state of a desired
electrical conductivity. The conductivity may be tailored by choice
of the wavelength of the incident electromagnetic radiation, as
well as the intensity and/or duration of the irradiation in each
selected wavelength, so that the composition may be used as a
semiconductor having a conductivity in the range from 10.sup.-6 to
10.sup.-3 S/cm. Typically, the passive, low-conductive state has a
conductivity of between 10.sup.-10 to 10.sup.-8 Scm.sup.-1.
[0022] The intensity and duration of the irradiation in each
wavelength can be varied, and a wide range of durations and
intensities are suitable for reversion between the passive and
active states. There exists a reversed relationship between the
duration and the intensity: the longer the irradiation the lower
the intensity needed to obtain the desired
luminescence/conductivity, and vice versa. By using a
high-frequency laser radiation, the state of the irradiated
location can be changed during one pulse of radiation (about
10.sup.-6 sec).
[0023] The term "stable" in the context of the present invention,
means that the composition of matter maintains its
lumninescent/conductive (generally, excited) properties essentially
unaltered, for prolonged periods of time. Preferably, the organic
composition of the present invention maintains each new electronic
state for a period of at least half a year.
[0024] The inventors have found now that irradiation of the
P4VPy/pyridine/water system with 250 nm leads, in addition to the
absorption band centered at 360 nm with a shoulder at 400 nm, to a
new red-shifted emission at 515 nm, and a weak absorption in the
visible (500-600 nm) and near IR ranges.
[0025] In other words, upon continuation of radiation at 250 nm,
together with an increase of the intensity of the absorption peak
at 360 nm, a prolonged tail through the whole visible range was
observed. Lower energy luminescent species are formed, and it is
believed that among these species are pyridine open form
photoproduct aggregates, such as polyazaacetylene (less than 1%
judging from the intensity of the absorption in the ranges 500-600
nm and 800-1400 nm). The presence of lower energy aggregates leads
to polymer morphology changes. Short-range aggregates enhance
polymeric units interaction, while long-range aggregates have a
tendency to crystallize forms similar to the comb-shaped polymers.
Also, depending on the polymer/liquid ratio, micelle-like forms
with the domain size over 200 nm and nanocrystals with average size
at 20-30 nm are formed.
[0026] The subsequent irradiation with 360 nm reverts the system
into its passive, substantially blue luminescent state.
[0027] Upon irradiation with 250 nm, the activation energy of the
pyridine ring cleavage and back reaction was evaluated as a
function of the polymer/pyridine/water ratio. Activation energy of
the pyridine ring cleavage in viscous polymeric solutions is in the
range of 0.6-4.0 Kcal/mol, depending on the pyridine concentration.
The value is lowered with increase of pyridine concentration.
Activation energy of the back reaction is significantly lower and
is in the range of 0.05-0.15 Kcal/mole.
[0028] When the P4VPy/pyridine system is irradiated with 380 nm,
new electronic states with lower energy band gap are formed, and as
a consequence--new red-shifted emissions appear. The initial stage
of the photochemical reaction consists of the interaction of
pyridinium ion, which appears in the system after polymer
dissolution, with pyridine molecules to thereby form poly-(4-vinyl
pyridinium/pyridine).
[0029] By applying UV-radiation of 250 nm or 380 nm to a film
comprising the P4VPy/pyridine composition located between two
spaced-apart electrodes, a conductive layer can be created in the
composition. The effect of the exciting wavelength causing the
desired conductivity of the film also depends on the film
thickness. The so-obtained conductive locations have conductivity
of at least 3-5 orders of magnitude greater than the conductivity
in the same location before irradiation.
[0030] The present invention further provides a method for treating
an organic composition comprising a water-soluble heteroaromatic
compound, water and a polymer containing one of repeating units
derived from six-membered aromatic heterocyclic monomers
substituted in the 4-position relative to the heteroatom by an
alkyl substituent, said six-membered aromatic heterocyclic monomer
optionally being further substituted, the method comprising:
[0031] (i) providing a viscous mixture of the constituents as
defined above;
[0032] (ii) irradiating at least a selected location of said
viscous mixture with ultra-violet radiation having a predetermined
intensity so as to cause excitation in the irradiated location of
said mixture to thereby obtain at least one of desired luminescence
or desired electrical conductivity of the irradiated location.
[0033] The invention also provides similar methods for obtaining
similar products, wherein the pyridine is replaced or is in
combination with another water-soluble heteroaromatic compound
having an even number of atoms in the ring, at least one of which
is a nitrogen, for example substituted pyridine, pyrimidine,
nicotine, quinoline, substituted quinoline, and bi-pyridine.
[0034] According to another aspect of the present invention, there
is provided an optical device comprising a cell containing an
organic composition comprising a water-soluble heteroaromatic
compound, water and a polymer containing repeat units derived from
six-membered aromatic heterocyclic monomers substituted in the
4-position relative to the heteroatom by an alkyl substituent, said
six-membered aromatic heterocyclic monomer optionally being further
substituted, said cell being shiftable between stable states of
different responses of said composition to predetermined incident
electromagnetic radiation.
[0035] Such an optical device may be used as an optical switch.
Alternatively, the optical device can be used as an information
carrier. By appropriately exciting selective locations in the
composition with predetermined electromagnetic radiation, a pattern
corresponding to specific information to be stored can be recorded
in the composition, and can then be read out, as well as erased, if
needed, by further excitation of the previously excited
(information carrying) locations by a different wavelength of
incident radiation. The optical device may include spatially
separated regions (e.g., layers) intended for ROM, recordable, and
WORM types of memory. To create a luminescent location (the
so-called "data region"), wavelengths of about 250 nm (e.g.,
250.+-.5 nm) and 380 nm (e.g., 380.+-.5 nm) can be used. To read
out the information, wavelengths in the range of about 460-600 nm,
e.g., 460 nm, 480 nm, 515 nm, 530 nm and 600 nm, can be used. To
remove the luminescence in this location (e.g., erase the data), a
wavelength of about 360 nm (e.g., 360.+-.2 nm) can be used.
[0036] The composition of the present invention may have further
varied utilities, in the construction of structures where it is
desired to manipulate (increase/decrease) the conductivity and/or
luminescence of a part of the structure by irradiation.
Furthermore, the composition of the present invention may be used
in various structures where it is desired to be able to reversibly
manipulate luminescence of components by irradiation.
[0037] One example is electric circuits, which can be produced by
coating electrodes transparent to UV-irradiation of 380 nm with the
composition of the invention (which is thus located between the
electrodes), and then exposing parts of this structure (by known
masking techniques) to the irradiation of certain wavelength in
order to produce high conductivity, and, if desired, exposing other
parts. Generally speaking, the present invention can be used in the
following:
[0038] optical tunable materials, optical ON/OFF switches;
[0039] electrophotography (the composition serving as a
photoreceptor, selective irradiation of the composition resulting
in recording a required charge pattern therein);
[0040] information storage device (selective irradiation of the
composition resulting in recording a pattern of data regions
indicative of the stored information);
[0041] photoinduced non-linear optic device with pyridine open ring
photoproduct-5-amino-2,4-pentadienal as a molecule with high
hyperpolarizability
[0042] Photoswitchable Organic Light Emitting Device (OLED).
BRIEF DESCRIPTION OF THE DRAWINGS
[0043] In order to understand the invention and to see how it may
be carried out in practice, a preferred embodiment will now be
described, by way of non-limiting example only, with reference to
the accompanying drawings, in which:
[0044] FIG. 1A schematically illustrates an optical device
utilizing the composition of the present invention that can operate
as an optical switch or a recordable optical memory device;
[0045] FIGS. 1B and 1C exemplify the use of the composition of the
present invention in a single-layer ROM device and a multi-layer
optical memory device, respectively;
[0046] FIG. 2 illustrates the energy schemes of composition sites
at initial (not irradiated) state, and the states obtained with two
different periods of UV-irradiations;
[0047] FIG. 3 shows the absorption spectra in UV/vis/NIR range of
poly(4-vinylpyridine)/pyridine/water mixture before and after 120
min UV-irradiation at 250 nm;
[0048] FIGS. 4A-4C show TEM images of the polymer gel film (A)
before irradiation and after UV irradiation at 250 nm (B and
C).
[0049] FIG. 5 illustrates the current vs. voltage curve of the
poly(4-vinylpyridine)/pyridine/water film before and after
UV-irradiation at 380 nm (I(A)-V/mV vs Ag/AgCl electrodes);
[0050] FIGS. 6A and 6B show the results of I-V dependence
measurement in the poly(4-vinylpyridine)/pyridine/water film
(ITO/ITO-electrodes) before and after the application of 380 nm
wavelength irradiation, respectively; and
[0051] FIG. 7 illustrates two examples of a transistor structure
utilizing the composition of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0052] The present invention provides a composition comprising a
water-soluble heteroaromatic compound, water and a polymer
containing repeat units derived from six-membered aromatic
heterocyclic monomers substituted in the 4-position relative to the
heteroatom by an alkyl substituent (the heterocyclic monomers being
optionally further substituted). The molar ratio between the
polymer, the water-soluble heteroaromatic compound and water is
preferably about 1:1:(0.3-1).
[0053] The water-soluble heteroaromatic compound may be pyridine,
substituted pyridine, pyrimidine, aqueous solution of nicotine,
quinoline, adenine, bi-pyridine, derivatives thereof or mixtures of
such compounds. The polymer may be optionally substituted
poly(4-vinyl pyridine), poly(4-vinyl quinoline) or co-polymers
thereof, preferably poly(4-vinyl pyridine).
[0054] Application of UV-radiation to the composition of the
present invention causes structural change in the composition.
Experiments have shown that the first stage of photosensitive
system formation is protonation of the polymeric pyridine and
physical interaction with neutral pyridine molecules by hydrogen
bonds. With continuation of the irradiation, this interaction is
prolonged and the density of the crosslinking increases. Changes of
emission properties of the location depend on the intensity and
duration of the applied radiation.
[0055] A very important feature of the composition of the present
invention is that the excited, luminescent location can be reverted
to its passive, non-luminescent state by applying UV-radiation of a
predetermined wavelength. Experiments have shown that such
luminescence-removing wavelength is about 360 nm (e.g., 360.+-.2
nm) with an energy of about 2.6-2.7 mW and more, and excitation
time of about 5-20 min.
[0056] The above features of the composition of the present
invention provide for using the composition as an optical medium in
an optical switch, which can be a simple ON/OFF switch, or a
tunable switch, since different wavelength responses can be
produced by exciting the medium with different wavelengths of
incident radiation.
[0057] FIG. 1A illustrates a cell 100A containing a layer 102 of
the composition of the present invention in a quartz or glass
container 104 transparent to predetermined electromagnetic
radiation. This cell can be used as an optical device, such as a
switch, or an optical memory device where the composition serves as
an information carrier. Thus, the device 100A can be a single-layer
optical memory device, which may be recordable or WORM (write once
read many) memory device. By exciting selective locations in the
layer with recoding radiation B.sub.1 of e.g. 250 nm, a pattern
corresponding to certain information can be recorded in the
composition, and can then be read out by exciting these locations
with reading radiation B.sub.2 of e.g., 400 nm, or can be erased by
exciting the data regions with 360 nm radiation B.sub.3.
[0058] FIG. 1B schematically illustrates an optical memory device
100B, which is a single-layer ROM (read only memory) device having
a data layer L formed by the composition of the present invention
in a quartz or glass container. The data layer L has spaced-apart
data regions, generally at 106, forming a pattern corresponding to
the stored information. This pattern has been recorded by applying
recording UV-radiation of e.g., 250 nm to the locations 106, and
can be read out by applying a different reading radiation
B.sub.read of e.g., 460 nm.
[0059] FIG. 1C schematically illustrates a multi-layer optical
memory device 100C, having several vertically aligned information
layers--three such layers L.sub.1, L.sub.2 and L.sub.3 being shown
in the figure. It should be understood that these layers may be
formed by vertically aligning three cells of the composition of the
present invention, or by a single cell of a certain suitable
thickness, considering the composition is in its semi-solid state.
In the present example of FIG. 1C, each layer has spaced-apart
luminescent data regions 106 created as described above to form a
pattern corresponding to the stored information. To read the
information, a reading laser beam is sequentially focused to each
of the layers. The first (lower) layer L.sub.1 can be initially
irradiated by 250 nm wavelength through the first quartz surface,
the second layer L.sub.2 irradiated by 380 nm, and the third upper
layer L.sub.3--by refocusing the 380 nm radiation thereto. A glass
surface between the adjacent layers can be used for protecting the
lower layer from short-UV irradiation. The reading of the
information from the different layers can be achieved by
irradiating the layers with the same wavelength (e.g., 400 nm),
that gives different responses from the layers excited (i.e.,
irradiated at the data recording stage with different wavelengths,
e.g., when using the exciting recording radiation of 250 nm and 380
nm, the 460 nm and 480 nm responses, respectively, can be
obtained). The erasing of the image (data) in one of the layers is
achieved by focusing 360 nm radiation on the respective layer.
[0060] Application of radiation of predetermined wavelength and
intensity or duration to the composition of the present invention
(at least to one or more locations therein) induces desired
electrical conductivity in the irradiated location(s). According to
the present invention, the formation of a conducting polymer is
achieved by photoinduced arrangement followed by covalent
interaction in the polymer system based on pyridine.
[0061] FIG. 2 illustrates energy schemes S.sub.1-S.sub.3 of the
same sample at different conditions. In the figures, VB is the
valence band and CB is the conduction band. Scheme S.sub.1
corresponds to the sample (or location) kept in dark, i.e. no
UV-radiation. Schemes S.sub.2 and S3 correspond to the samples (or
locations) after, respectively, 30 minutes and 1 hour
UV-irradiation. In the present example, the conductivity changes in
the sample were achieved by irradiating the sample by a Xenon short
ARC lamp with 380 nm wavelength (7 mW) for 30 or 60 min. It should
however be noted that by using laser irradiation of a power range
of a few Watts, irradiation duration of milliseconds is sufficient
to achieve the same results. The effect of increased electrical
conductivity induced by UV-radiation can be explained as follows:
photoinduced interchain interactions lead to electron density
delocalization, and simultaneous decrease of the energy band gap
.DELTA.E.sub.g of the material with the increase of the
crosslinking density.
[0062] The following are two examples of preparation of the
composition for measuring electrical conductivity thereof induced
by incident radiation.
EXAMPLE 1
[0063] 1 g of dry poly(4-vinyl pyridine) P4Vpy) (dried under vacuum
(10.sup.-3 torr) at 40-60.degree. C. for one week) was dissolved in
0.8-1.0 ml pyridine/water solution with molar ratio between
pyridine and water molecules 0.3:1 in a glass bottle at the room
temperature.
[0064] The polymer used had a MW of 10000-50000 (Polyscience, Co.).
Pyridine high purity (anhydrous 99.8% (Aldrich)) and deionized
triply distilled water with pH=6.5-7 were used.
[0065] The resultant viscous solution was degassed and placed
between two ITO covered glass electrodes for conductivity
measurements. The optical density of the ITO electrodes suitable
for treatment with 380 nm-radiation is 0.15. The size of the
electrodes area, which was covered by polymer's solution was 25
mm.times.25 mm. To obtain samples with reproducible thickness of
20.+-.5 .mu.m , the two electrodes were pressed by 200 g/cm.sup.2
and kept under this pressure for 15 min. The polymer solution
confined between the electrodes was irradiated for 30-60 minutes by
long UV-irradiation centered at 380 nm using Xenon short ARC lamp
having energy of 7 mW/cm.sup.2. The conductivity of 10.sup.-3
Scm.sup.-1 was achieved. The similar value of the photoinduced
conductivity can be achieved with more powerful source of UV-light
at 380 nm wavelength. The estimation regarding the quantum yield of
the photochemical reaction showed that similar conductivity changes
can be achieved with laser irradiation (having a power of 5-7
W/cm.sup.2) with a duration of millisecond time-scale.
EXAMPLE 2
[0066] 1 g of poly(4-vinyl pyridine) (P4Vpy) dried under vacuum
(10.sup.-3 torr) at 40-60.degree. C. for one week was dissolved in
0.8-1.0 ml pyridine/water solution with molar ratio between
pyridine and water molecules 1:(0.3-1.0) in a glass bottle at the
room temperature. The polymer used had a MW of 10000-50000
(Polyscience, Co.). Pyridine high purity (anhydrous 99.8%
(Aldrich)) and deionized triply distilled water with pH=6.5-7.0
were used.
[0067] The resultant viscous solution was degassed and placed
between two electrodes for conductivity measurements. Cr--Au
covered quartz (Nanonics, Co) and ITO covered glass (Delta
Technologies) electrodes were used. The optical density of Cr--Au
electrodes in the 380 nm wavelength range is 0.6-0.7. The size of
the electrodes area, which was covered by polymer's solution, was
25 mm.times.25 mm. To obtain samples with reproducible thickness of
20.+-.5.0 .mu.m, the two electrodes were pressed by 200 g/cm.sup.2
and kept under this pressure for 15 min. The polymer film confined
between the said electrodes was irradiated by short UV irradiation
in the range of 380.+-.5 nm for 1 hour using a Xenon low pressure
lamp the conductivity 10.sup.-6 Scm.sup.-1 was obtained. When using
laser irradiation of the same wavelength with power of several
W/cm.sup.2, similar conductivity changes can be achieved with the
irradiation duration of the microsecond scale.
[0068] The films prepared in Examples 1 and 2 above are
characterized by the photoinduced directional ordering through the
charge transfer between pyridine and pyridinium as free as well as
bounded. During this photoinduced ordering in comparatively thin
layer of the material the conductive channel can be formed.
[0069] SHG experiments were performed on thin film (3 .mu.m)
poly(vinylpyridine)/pyridine/water samples which were irradiated at
250 nm for 6 hours, dried (10 h, 110.degree. C., 10.sup.-3 torr)
and then corona poled (3.5 kV, 140.degree. C., nitrogen atmosphere,
30 min). The film SHG efficiency was found as corresponding to
d.sub.eff.about.0.1 pM/V, evidencing the formation of nonlinear
moieties of cleaved pyridine such as aminopentadienal and
polyazaacetylene in the film albeit at a low concentration.
[0070] The existence of polyazaacetylene or head-to-tail
aminopentadienal organization can be deduced from the absorption
spectra of the composition as shown in FIG. 3. Irradiation of
viscous films containing poly-(4-vinylpyridine)/pyridine/water
mixture (1:1:0.3 molar ratio between poly-(4-vinylpyridine)
repeating units, pyridine and water molecules) at 250 nm leads to
their partial solidification. The changes can be easily followed by
UV/Vis/NIR spectroscopy. Graph G.sub.1 presents the absorption
spectrum of the composition prior to being irradiated, and graph
G.sub.2 shows the absorption spectra of the composition in the
UV/Vis/NIR range after a 120 min irradiation at 250 nm. As shown, a
new broad absorption band appeared between 320 nm and 600 nm with a
maximum at 360 nm and a shoulder at 400 nm, and another weak
absorption band was observed in the visible and near IR range
(insert).
[0071] The absorption spectra of the P4VPy/pyridine system can be
interpreted as follows:
[0072] 1) the band at 360 nm steams from open form pyridine
photoproduct;
[0073] 2) the shoulder at 400 nm steams from the aminopentadienal
moiety;
[0074] 3) the weak absorption in the visible (500-600 nm) and NIR
ranges can be explained by formation of small amounts of
polyazaacetylene of formula (I) below, or long-chain
aminopentadienal aggregates, or crosslinking through the open form
photoproduct interchain interaction: 1
[0075] wherein
[0076] n is an integer between 2 and 10;
[0077] i is an integer between 1 and n; and
[0078] the various R.sub.is and R' are independently H or a
vinyl-group of a poly(4-vinyl pyridine) polymeric chain.
[0079] Indeed, in a viscous media when aminopentadienal moieties
attached to the polymer are brought closely together, linear
oligomers can be formed considerably easier than in dilute
solutions. Aminopentadienal molecules stemming from pyridine
cleavage, can act as cross-linkers.
[0080] Quantum mechanical calculations of the spectra of
polyazaacetylene of formula I, wherein R' and R.sub.i are hydrogen
and n is between 1 to 5, at the semiempirical ZINDO/AM1 level,
showed that energy of the longest wave transition converges when n
increases, whereas the energies of the shorter wave transitions
undergo red shifts proportional to the n value. The intensity of
the longest wave absorption is predicted to be very high for the
planar model and drastically diminishes on coplanarity distortion.
Although it is difficult to expect coplanarity of monomeric units
in a relatively rigid solid polymeric system, the amount of the
polyazaacetylene of formula (I) should be small (less than 1%)
judging by the intensity of the absorption in the ranges of 500-600
nm and 800-1400 nm.
[0081] Irradiation also brings about a gradual shift of emission
from 440 nm to 600 nm.
[0082] Together with formation of the luminescent aggregates,
changes were also observed in the polymer morphology. TEM and
calorimetry studies were applied for the polymer morphology
investigation.
[0083] Transmission electron microscopy (TEM) was carried out on
samples obtained from the gel thin film before and after
irradiation at 250 nm for 60 min. The TEM image of the gel before
irradiation is presented in FIG. 4A including insert, in two
scales: with low and high magnification, where homogeneous
structure of the polymer film is observed. The photoinduced process
of formation of micelles and nanocrystals in the pyridine-based
polymeric system was achieved upon prolonged UV irradiation at 250
nm. The TEM image of the micelles is presented in FIG. 4B, while
that of the nanocrystals is presented in FIG. 4C.
[0084] The micelles with the size in the range of 200 nm and the
nanocrystals with the average size 20-30 nm are two kinds of the
phase-separated structures, which also characterized the gel after
UV-irradiation. The electron diffraction pattern of the typical
nanocrystal clearly indicates the concentric ring diffraction
pattern and Bragg spots.
[0085] Under UV-irradiation centered at 250 nm or 380 nm,
poly-(vinyl pyridine)/pyridine/water solution change conductivity
depending on the composition contents and the thickness of the
composition layer. Most probable explanation of the phenomenon is
in the photoinduced free and bounded pyridine ordering through the
photoinduced proton transfer between neutral pyridine and
pyridinium as free as bounded with formation of the conductive
channels in a case of irradiation with 380 nm and covalent bonding
in a case of irradiation with 250 nm.
[0086] The conducting properties of the polymer solutions of the
present invention before and after UV-irradiation were compared. To
evaluate the conducting properties, the following three methods
were used.
[0087] Current measurement in the circuit. In this method, the
composition (polymer solution) was placed in the cell constructed
from two slides: quartz slide covered by a gold layer (thickness
0.4 .mu.m with OD 0.6-0.7 at 380 nm) and glass slide covered with
ITO. The Sweep Function Generator (Escort) was used as a source of
voltage (10 Hz, 3,6 V) to avoid electrode polarization, and
Keithley 237 and model 197 was used as a current source.
[0088] Cyclic voltammetry (CV) measurement (I. Turyan, D. Mandler,
J. Am. Chem. Soc., 1998 (120, pp. 10733-10742) in a range of
-1.0+1.0 V.
[0089] I-V dependence by application of the Source-Measurement Unit
Keithley 237.
[0090] FIGS. 5, 6A-6B graphically illustrate the results of the
above experiments. As shown in FIG. 5 (results of method B with V
vs Ag/AgCl electrodes), before irradiation (graph P.sub.1), the
conductivity of the 20 .mu.m film of
poly(4-vinylpyridine)/pyridine/water was 1.2.times.10.sup.-8
Scm.sup.-1. After UV-irradiation (graph P.sub.2) with a wavelength
of 380 nm during 30 min, the conductivity increased to
0.8.times.10.sup.-4 Scm.sup.-1. This electric conductivity of the
film was stable during 12 months period of storage. Conductivity of
10.sup.-6 Scm.sup.-1 was obtained when a similar film with a
thickness of about 3 .mu.m was irradiated with 250 nm
radiation.
[0091] FIG. 6A shows the I-V dependence (measured with method C) of
the thin film of poly(4-vinylpyridine)/pyridine/water
(Cr--Au/ITO-electrodes) before the application of UV-radiation. The
initial conductivity (before irradiation) was evaluated as
2.3.times.10.sup.-6 Scm.sup.-1. Slight ionic conductivity
characterizes the conductivity properties of the film. FIG. 6B
illustrates the I-V dependence of the same film after 1 hour of the
380 nm wavelength UV-irradiation (Cr--Au/ITO electrodes). The
conductivity of the film was estimated as 7.times.10.sup.-3
Scm.sup.-1. When using a laser source with power of the beam in the
range of W/cm.sup.2, it is possible to achieve the same
conductivity change with the irradiation duration of microsecond
scale.
[0092] The average value (43 experiments) of the conductivity
before irradiation of the polymer solution thin film of
poly(4-vinylpyridine)/py- ridine/water was estimated as
2.5.times.10.sup.-8 Scm.sup.-1. The average value (23 experiments)
of the conductivity change in the case of the long wave range of UV
irradiation (380 nm) was estimated as 6.3.times.10.sup.-4
Scm.sup.-1. The average value (20 experiments) in the case of the
short wavelength UV-irradiation (250 nm) was estimated as
7.2.times.10.sup.-5 Scm.sup.-1.
[0093] Additionally, the experiments have shown that increasing the
content of water in the composition decreases the initial
conductivity thereof (i.e., prior to being irradiated by
UV-radiation).
[0094] The following polymer/solvent compositions were tested
(method A) on the photoinduced conducting properties:
[0095] 1. (a) Poly(2-vinyl pyridine)/EtOH and (b) Poly(2-vinyl
pyridine)/Py;
[0096] 2. (a) Poly vinyl pyrrolidone/EtOH and (b) Poly vinyl
pyrrolidone/Py;
[0097] 3. (a) Poly(4-vinyl pyridine-co-butylmethacrylate)/EtOH and
(b) Poly(4-vinyl pyridine-co-butylmethacrylate)/Py and
[0098] 4. (a) Poly(4-vinyl pyridine)/EtOH and (b) Poly(4-vinyl
pyridine)/Py.
[0099] TV-irradiation of the compositions 1(a) and 1(b) resulted in
the conductivity change by the factors of 0.91 and 1.2,
respectively. Irradiation of the compositions 2(a) and 2(b)
resulted in the conductivity change by factors 1.25 and 1.05,
respectively. Irradiation of the compositions 3(a) and 3(b)
provided the conductivity changes by factors 1 and 17.1,
respectively. The similar treatment of the composition 4(a)
provided the conductivity increase by factor of 1.38. Poly(4-vinyl
pyridine)/Py (composition 4b) showed the conductivity change from
3.6.times.10.sup.-8 Scm.sup.-1 before irradiation to
1.8.times.10.sup.-5 Scm.sup.-1 after irradiation (ratio of
5000).
[0100] The composition of the present invention can thus be used,
for example, in electrophotography, serving as a photoreceptor on
which a latent electrostatic image (charge pattern) can be created
by applying UV-radiation, for example 250 nm, to corresponding
locations in the composition.
[0101] The composition of the present invention can also be used in
a transistor device. FIG. 7 schematically illustrate a transistor
structure 200 fabricated by integrated technology to define three
electrodes--base electrode E.sub.base located on top of a substrate
layer L.sub.0 and coated by an insulating layer L.sub.ins
(SiO.sub.2), emitter and collector electrodes E.sub.em and
E.sub.col arranged in a spaced-apart relationship on top of the
insulating layer and coated by the composition L.sub.com of the
present invention. A semiconductor region R.sub.sem in a space
between the electrodes E.sub.em and E.sub.col is then created by
irradiating the respective location in the composition with a 380
nm radiation.
[0102] The composition of the present invention can also be used in
photoinduced non-linear optic (NLO) devices. NLO waveguides can be
defined by UV irradiation, and OLEDs' 480 nm emission can be turned
to 515 nm wavelength by irradiation with UV-light at 380 nm. The
emission wavelength of the device can be altered in real time by UV
irradiation.
[0103] Those skilled in the art will readily appreciate that
various modifications and changes can be applied to the embodiments
of the invention as herein before exemplified without departing
from its scope defined in and by the appended claims.
* * * * *